Multiple-input multiple-output radio transceiver

ABSTRACT

A MIMO radio transceiver to support processing of multiple signals for simultaneous transmission via corresponding ones of a plurality of antennas and to support receive processing of multiple signals detected by corresponding ones of the plurality of antennas. The radio transceiver provides, on a single semiconductor integrated circuit, a receiver circuit or path for each of a plurality of antennas and a transmit circuit or path for each of the plurality of antennas. Each receiver circuit downconverts the RF signal detected by its associated antenna to a baseband signal. Similarly, each transmit path upconverts a baseband signal to be transmitted by an assigned antenna.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/707,744 filed Jan. 8, 2004, which is a continuation of U.S. patentapplication Ser. No. 10/065,388 filed on Oct. 11, 2002, which issued asU.S. Pat. No. 6,728,517 on Apr. 27, 2004, which claims the benefit ofU.S. Provisional Patent Applications 60/319,434 filed Jul. 30, 2002,60/319,360 filed Jun. 27, 2002, 60/319,336 filed Jun. 21, 2002,60/376,722 filed Apr. 29, 2002, and 60/374,531 filed Apr. 22, 2002,which are incorporated by reference as if fully set forth.

FIELD OF INVENTION

This application is related to wireless communications.

BACKGROUND

A primary goal of wireless communication system design is to use theavailable spectrum most efficiently. Examples of techniques to increasespectral efficiency include coded modulation techniques such as turbocodes and trellis-coded modulation, and multiple access techniques suchas code division multiple access (CDMA).

Yet another way to optimize spectral efficiency that has recently becomepopular in the academic community is the use of MIMO radio systems. MIMOradio communication techniques have been proposed for use in, forexample, 3G mobile telephone systems. However, prior efforts to exploitthe benefits of a MIMO system have failed because, among other reasons,a cost-effective MIMO radio could not be developed.

SUMMARY

A MIMO radio transceiver is provided to support processing of multiplesignals for simultaneous transmission via corresponding ones of aplurality of antennas and to support receive processing of multiplesignals detected by corresponding ones of the plurality of antennas. TheMIMO radio transceiver is one that is suitable for a highly integratedand low cost fabrication. In addition, the radio transceiver can performMIMO transmit and receive operation in a portion of an RF band, up tosubstantially the entire RF band. The multiple transmit and receivepaths are particularly useful to support joint maximal ratio combiningtechniques, also referred to herein as composite beamforming (CBF).

The radio transceiver provides, on a single semiconductor integratedcircuit, a receiver circuit or path for each of a plurality of antennasand a transmit circuit or path for each of the plurality of antennas.Each receive path downconverts the RF signal detected by its associatedantenna to a baseband signal, using either a direct-conversion processor a super-heterodyne (multiple conversion) process. Similarly, eachtransmit circuit upconverts a baseband signal to be transmitted by anassigned antenna, using either a direct up-conversion process or amultiple-stage conversion process.

The multiple receive and transmit paths are integrated onto the samesemiconductor integrated circuit. This provides significant cost andspace/area savings. One use of this type of radio transceiver is toreceive and transmit signals that, at baseband, are processed using theaforementioned CBF techniques (whereby weighted components of a signalare sent via each of a plurality of antennas and received at the otherdevice by one or more antennas) to enhance the link margin with anothercommunication device. In such an application, it is very important thateach of the receive processing paths and each of the transmit processingpaths be matched in terms of amplitude and phase response. Because themultiple receive and transmit paths are integrated into a singlesemiconductor die, the processing paths will inherently be better phaseand amplitude matched, and any effects resulting from semiconductorintegration will track among the processing paths. Moreover, anyoperational changes due to temperature variations will also better trackamong the processing paths because they are integrated into the samesemiconductor integrated circuit.

Low cost radio transceiver solutions are provided that, for example, donot require intermediate frequency (IF) filters, have power amplifiersintegrated on the radio transceiver integrated circuit (IC), use onefrequency synthesizer, and integrate various control switches fortransmit/receive and band select operations.

The above and other advantages will become more apparent with referenceto the following description taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1 is a general block diagram of a radio transceiver having multipleprocessing paths for multiple-input multiple-output (MIMO).

FIG. 2 is a schematic diagram of a MIMO radio transceiver having asuper-heterodyne architecture.

FIG. 3 is a schematic diagram of a MIMO radio transceiver having avariable intermediate frequency architecture.

FIG. 4 is a schematic diagram of a MIMO radio transceiver having adirect-conversion architecture.

FIG. 5 is a schematic diagram of radio front-end section useful with aMIMO radio transceiver.

FIGS. 6-8 are schematic diagrams showing alternative radio front-endsections used with a MIMO radio transceiver.

FIG. 9 is a schematic diagram of still another radio-front end useful inconnection with two radio transceiver ICs in a single device to provide4 transmit and receive paths.

FIG. 10 is a schematic diagram of yet another radio front-end sectionuseful in connection with a single radio transceiver IC that provides 4transmit and receive paths.

FIGS. 11 and 12 are diagrams showing how digital-to-analog convertersand analog-to-digital converters may be shared in connection with a MIMOradio transceiver.

FIGS. 13 and 14 are diagrams showing how filters in the radiotransceiver can be shared so as to reduce the area of an integratedcircuit.

DETAILED DESCRIPTION

When referred to hereafter, the terminology “wireless transmit/receiveunit (WTRU)” includes but is not limited to a user equipment (UE), amobile station, a fixed or mobile subscriber unit, a pager, a cellulartelephone, a personal digital assistant (PDA), a computer, or any othertype of user device capable of operating in a wireless environment. Whenreferred to hereafter, the terminology “base station” includes but isnot limited to a Node-B, a site controller, an access point (AP), or anyother type of interfacing device capable of operating in a wirelessenvironment.

FIG. 1 shows a block diagram of a radio transceiver 10. The radiotransceiver 10 is suitable for processing radio frequency signalsdetected by at least two antennas. The foregoing description is directedto an embodiment with two antennas 12 and 14, and an associated transmitand receive path for each, but this same architecture can be generalizedto support in general N processing paths for N-antennas. This radiotransceiver architecture is useful to support the aforementioned CBFtechniques. CBF systems and methods are described in U.S. patentapplication Ser. No. 10/164,728, filed Jun. 19, 2002 entitled “Systemand Method for Antenna Diversity Scheme Using Joint Maximal RatioCombining;” U.S. patent application Ser. No. 10/174,689, filed Jun. 19,2002, entitled “System and Method for Antenna Diversity Using Equal GainJoint Maximal Ratio Combining;” and U.S. patent application Ser. No.10/064,482, filed Jul. 18, 2002 entitled “System and Method for JointMaximal Ratio Combining Using Time-Domain Signal Processing.” Theseco-pending and commonly assigned patent applications all relate tooptimizing the received SNR at one communication based on the transmitvector used at the other communication device.

One advantage of the technology described in the aforementioned patentapplication entitled “System and Method for Antenna Diversity UsingEqual Gain Joint Maximal Ratio Combining” is that the output powerrequired from each antenna path is reduced. Therefore, the size of thepower amplifiers can be reduced, which reduces the overall semiconductorchip area of the IC, and makes it easier to isolate other RF circuitryon the IC from the power amplifiers.

The radio transceiver 10 comprises a receiver and a transmitter. Thereceiver comprises receiver circuits 20 and 30. There is a receivercircuit or section 20 for antenna 12 and a receive circuit or section 30for antenna 14. Similarly, the transmitter comprises a transmit circuit40 for antenna 12 and a transmit circuit 60 for antenna 14. Eachreceiver circuit 20 and 30 includes a downconverter 24, a variablelowpass filter 26 and a sample-and-hold circuit 28. Each transmitcircuit 40 and 60 includes a sample-and-hold circuit 42, a low passfilter 44, an upconverter 46, a bandpass filter 48 and a power amplifier50. The downconverters 24 may involve circuits to perform single-stage(direct) conversion to baseband or two-stage conversion to anintermediate frequency, then to baseband. Likewise, the upconverters 46may upconvert directly to RF or to an intermediate frequency, then toRF. More specific embodiments are described hereinafter in conjunctionwith FIGS. 2-4. The lowpass filters 44 may be variable filters toaccommodate a narrowband transmit mode of operation or one of severalwideband transmit modes of operation.

A front-end section 90 couples the radio transceiver 10 to antennas 12and 14. There are switches 62 and 64 coupled to antennas 12 and 14,respectively. Switch 62 selects whether the output of the transmitcircuit 60 or the input to the receiver circuit 20 is coupled to antenna12. Switch 64 selects whether the output of the transmit circuit 40 orthe input of the receiver path 30 is coupled to antenna 14. There arebandpass filters 22 coupled to one switch terminal of the switches 62and 64, respectively. In addition, there are lowpass filters 52 and 54coupled between the output of the power amplifiers 50 in each transmitcircuit 40 and 60, and, the other switch terminal of the switches 62 and64, associated with antennas 12 and 14, respectively.

The outputs of the sample-and-hold circuits 28 of receiver circuits 20and 30 are coupled to analog-to-digital converters (ADCs) 70 and 72,respectively. The inputs to the sample-and-hold circuits 42 in thetransmit circuits 40 and 60 are coupled to digital-to-analog converters(DACs) 80 and 82, respectively. The DACs 80 and 82 may receive as inputfirst and second digital baseband transmit signals representingcomplex-weighted transmit signal components of a single baseband signalto be transmitted simultaneously from antennas 12 and 14. The first andsecond transmitter circuits 40 and 60 process the first and secondanalog baseband signals for transmission substantially simultaneously.Likewise, antennas 12 and 14 may detect first and second receivesignals, respectively, which are components of a single signal that wastransmitted to transceiver 10. The first receiver circuit 20 and thesecond receiver circuit 30 process the first and second receive signalssubstantially simultaneously to allow for a weighted combining of theresulting digital baseband receive signals.

An interface and control block 92 is provided that interfaces the radiotransceiver 10 with other components, such as a baseband processingsection. For example, the interface and control block 92 receives afilter bandwidth control signal, a center frequency control signal, andswitch control signals, all of which are used to control operation ofcertain components in the radio transceiver. Alternatively, theaforementioned signals may be sourced for a control processor orbaseband section and coupled directly to pins that are tied to theappropriate components of the transceiver 10.

The center frequency control signal controls the center frequency of thelocal oscillator signals used by the downconverters 24 in each receivercircuit 20 and 30 and of the upconverters 46 in each transmit circuit 40and 60. In addition, the filter bandwidth control signal controls thecut-off frequency of the variable lowpass filters 26. The switch controlsignals control the position of the switches 62 and 64 depending onwhether the transceiver 100 is receiving or transmitting.

One distinctive function of the radio transceiver 10 is tosimultaneously receive and process signals detected by each antenna 12and 14, in order to output first and second baseband receive signalsthat are combined appropriately using the aforementioned CBF techniques(in a baseband processor) to obtain a received signal. Conversely, theradio transceiver 10 simultaneously processes first and second basebandanalog transmit signals (representing weighted components of a singletransmit signal) and outputs them for transmission via antennas 12 and14, respectively. The radio transceiver 10 shown in FIG. 1 can beoperated in a half-duplex mode or, if desired, a full-duplex mode.

Moreover, the radio transceiver 10 may perform MIMO operation in avariable bandwidth. For example, the radio transceiver 10 may transmitor receive a signal in a single RF channel in a radio frequency band,such as a 20 MHz 802.11 channel of the 2.4 GHz band. However, it mayalso perform MIMO operation to transmit or receive a signal in a widerbandwidth, such as a higher data rate signal or signals that occupy upto substantially an entire frequency band, such as 80 MHz of the 2.4 GHzband. The filter bandwidth control signal sets the cut-off frequency ofthe lowpass filters 26 in each receiver circuit 20 and 30 to lowpassfilter the desired portion of RF bandwidth. The radio transceiver 10also has a receive-only non-MIMO operation where the output of eitherreceive path can be taken to sample any part or the entire RF band, byadjusting the lowpass filters 26 accordingly. This latter functionalityis useful to obtain a sample of a RF band to perform spectrum analysisof the RF band. As is explained in further detail in connection withFIGS. 13 and 14, the lowpass filters 44 in the transmitter may beeliminated and the variable lowpass filters 28 used for both receivedsignals and transmit signals.

The large dotted box around the receiver circuits 20 and 30 and thetransmit circuits 40 and 60 is meant to indicate that all of thesecomponents, including the power amplifiers 50, may be implemented on asingle semiconductor integrated circuit (IC). Other components may alsobe implemented on the IC as semiconductor and filter design technologyallows. The performance advantages achieved by integrating multipletransmit paths and multiple receive paths on the same semiconductor aredescribed above.

FIGS. 2-4 show more specific examples of the MIMO radio transceivershown in FIG. 1. FIG. 2 shows a dual-band radio transceiver employing asuper-heterodyne (two-stage) conversion architecture. FIG. 3 shows adual-band radio transceiver employing a walking intermediate frequency(IF) conversion architecture using only one frequency synthesizer. FIG.4 shows a dual-band radio transceiver employing a direct conversion(single-stage) architecture. FIG. 5 illustrates a radio-front endsection that can be used with any of the radio transceivers shown inFIGS. 2-4.

With reference to FIG. 2 in conjunction with FIG. 5, radio transceiver100 will be described. The radio transceiver 100 shown in FIG. 2 is asuper-heterodyne receiver that is capable of operating in two differentfrequency bands, such as, for example, the 2.4 GHz unlicensed band andone of the 5 GHz unlicensed bands.

As shown in FIG. 5, the radio transceiver 100 is designed to be coupledto first and second antennas 102 and 104 via a RF front end section 105that includes transmit/receive (T/R) switches 106 and 108, which coupleto antennas 102 and 104, respectively. Each T/R switch 106 and 108 hasan antenna terminal to be coupled to its associated antenna, a receiveoutput terminal and a transmit input terminal and is responsive to T/Rswitch control signals to select either the receive output terminal orthe transmit input terminal, depending on whether the radio transceiveris transmitting or receiving. Also in the RF front end section 105 areband select switches 110, 112, 114 and 116 that select the output of theantenna from switches 106 and 108 depending in which frequency band asignal is being transmitted or received. Band select switches 110 and112 are receive band select switches, each of which has an inputterminal coupled to the receive output terminals of the first and secondT/R switches 106 and 108, respectively, and a first output terminalcoupled to the BPFs 120 and 124 respectively, and a second outputterminal coupled to the BPFs 122 and 126 respectively. Band selectswitches 114 and 116 are transmit band select switches and each hasfirst and second input terminals and an output terminal. The first inputterminals of band select switches 114 and 116 are connected to LPFs 128and 132, respectively, and the second input terminals of switches 115and 116 are connected to LPFs 130 and 134, respectively. The outputterminals of switches 114 and 116 are coupled to the transmit inputterminals of the first and second T/R switches 106 and 108,respectively.

Referring back to FIG. 2, on the receive side of the radio transceiver100, there is a receiver comprising a receiver path or circuit 140associated with signals detected by antenna 102 and a receiver path orcircuit 170 associated with signals detected by antenna 104. On thetransmit side, there is a transmitter comprising a transmit path orcircuit 210 associated with antenna 102 and a transmit path or circuit230 associated with antenna 104. Each of the receiver circuits 140 and170 has two branches: a first branch to process a signal from a firstradio frequency band, and a second branch to process a signal from asecond radio frequency band.

More specifically, each branch in the receiver circuits 140 and 170 iscoupled to a corresponding one of the bandpass filters 120, 122, 124 or126 in the RF front end section 105 shown in FIG. 5. In a first branchof the receiver circuit 140, there is a low noise amplifier (LNA) 142and an RF mixer 144 to downconvert an RF signal from a first radiofrequency band (RFB1) to an intermediate frequency (IF). In a secondbranch of the receiver circuit 140 there is an LNA 152 and an RF mixer154 that downconverts an RF signal from a second radio frequency band toIF. An IF filter (IFF) 145 is coupled to the mixer 144 and to the mixer154, and on the output side of the IFF 145 is a variable amplifier 146,quad mixers 148 and 156 and a variable lowpass filters 150 and 158. Asample-and-hold circuit 160 is coupled to variable lowpass filter 150and a sample-and-hold circuit 162 is coupled to variable lowpass filter158. As will be described in more detail hereinafter, the first branchof receiver circuit 140 (consisting of LNA 142 and mixer 144) processesa signal from a first RF band (RFB1) detected by antenna 102. The secondbranch of receiver circuit 140 (consisting of amplifier 152 and mixer154) processes a signal from a second RF band (RFB2) detected by antenna102. Only one of the branches of receiver circuit 140 is operating atany given time. As a result, the IFF 145 and the variable poweramplifier 146 can be shared by the branches (without the need for anadditional switch) assuming the output impedance of the mixers 144 and154 is high. The quad mixers 148 and 156 generate an in-phase signal (I)and a quadrature-phase (Q) signal of the signal supplied to the input ofthe variable amplifier 146. Thus, to summarize, the receiver circuit 140has a first downconverter consisting of an RF mixer (144 or 154,depending on what band branch is being used) that down-mix a firstreceive signal detected by antenna 102 (FIG. 5) to an intermediatefrequency signal, and quad mixers 148 and 156 that further down-mix theintermediate frequency signal to I and Q baseband analog signals.

The receiver circuit 170 has components 172 through 192 that mirrorthose in the receiver circuit 140, but are used to process a signal fromantenna 104 (FIG. 5) in either the first RF band (RFB1) or the second RFband (RFB2). Like receiver circuit 140, receiver circuit 170 has asecond downconverter consisting of an RF mixer (174 or 184, depending onwhat band branch is being used) that down-mixes a second receive signaldetected by antenna 104 to a second intermediate frequency signal at thesame IF as the first intermediate frequency signal produced in receivercircuit 140, and quad mixers 178 and 186 that further down-mix thesecond IF signal to I and Q baseband analog signals.

Switches 200 and 202 are coupled to the sample-and-hold circuits inreceiver circuits 140 and 170, respectively, to switch between the I andQ outputs associated with the first and second analog baseband receivesignals output by receiver circuit 140 and receiver circuit 170,respectively, for processing by an ADC. In addition, switches 270 and280 serve the additional function on the transmit side to receive asinput the output of DACs that supply first and second analog basebandsignals to be transmitted.

On the transmit side of the radio transceiver 100 there are two transmitcircuits 210 and 230. In transmit circuit 210, there are quad mixers 212and 214 coupled to receive as input the I and Q data signals,respectively, that up-mix these signals by an intermediate frequencylocal oscillator signal to an IF. The outputs of the quad mixers 212 and214 are summed and coupled to the variable amplifier 216, which in turnis coupled to an RF mixer 218. The RF mixer 218 upconverts theintermediate frequency signal to RF, in either RFB1 or RFB2. Bandpassfilters 222 and 224 are coupled to the output of the mixer 218. Bandpassfilter 222 is associated with RFB1 and bandpass filter 224 is associatedwith RFB2. There is a power amplifier 226 coupled to the output of thebandpass filter 222 and a power amplifier 228 coupled to the output ofbandpass filter 228. The output of power amplifier 226 is coupled to theinput of the lowpass filter 128 (FIG. 5) and the output of poweramplifier 228 is coupled to the input of the lowpass filter 130 (FIG.5). To summarize, the first transmit circuit 210 has an upconverterconsisting of the quad mixers 212 and 214 that up-mix the baseband I andQ signals representing the first transmit signal, and the RF mixer 218that further up-mixes the intermediate frequency signal to produce afirst RF signal that is to be coupled to the first antenna 102 (FIG. 5).The output of the RF mixer 218 is coupled to bandpass branchesconsisting of BPF 222 and power amplifier 226 or BPF 224 and poweramplifier 228.

The transmit circuit 230 associated with antenna 104 has components 232through 248 and mirrors transmit circuit 210 to process a secondtransmit signal component. Similar to the first transmit circuit 210,the second transmit circuit 230 has an upconverter consisting of quadmixers 232 and 234 that up-mix I and Q baseband signals representing thesecond transmit signal, and an RF mixer 238 that further-up mixes theintermediate frequency signal to produce a second RF signal that iscoupled to the second antenna 104 (FIG. 5) for transmissionsubstantially simultaneous with the first RF signal.

The input signals to the transmitter circuits 210 and 230 are suppliedfrom DACs (not shown) to switches 270 and 280 that alternately selectbetween baseband I and Q signals, which are coupled to respectivesample-and-hold circuits 272 and 274 (in transmitter circuit 210) andsample-and-hold circuits 282 and 284 in transmitter circuit 230.Sample-and-hold circuits 272 and 274 are in turn coupled to LPFs 276 and278, respectively, and sample-and-hold circuits 282 and 284 are coupledto LPFs 286 and 288, respectively. LPFs 276 and 278 filter the basebandI and Q signals of the first transmit signal and supply their output tothe quad mixers 212 and 214, respectively. Likewise, the LPFs 282 and288 filter the baseband I and Q signals of the second transmit signaland supply their output to the quad mixers 232 and 234, respectively.The number of LPFs may be reduced if the variable LPFs in the receiverare shared are used for receive processing and transmit processing. Onetechnique for sharing the variable LPFs for transmit and receiveoperation is shown in FIGS. 13 and 14.

Since radio transceiver 100 is a super-heterodyne device, RF localoscillator signals for the radio frequencies associated with RFB1 andRFB2 and IF local oscillator signals need to be generated. To this end,there is an IF synthesizer (IF LO synth) 250 and a voltage controlledoscillator (VCO) 252 (including a 90° phase component, not shown forsimplicity) to generate in-phase and quadrature phase IF localoscillator signals that are coupled to the mixers 148, 156, 178 and 186,and to mixers 212, 214, 232 and 234. There is an RF local oscillatorsynthesizer (RF LO synth) 260 coupled to VCOs 262, 264 and 266 thatsupply different RF local oscillator signals to mixers 144, 154, 174 and184 on the receive side and to mixers 218 and 238 on the transmit side.There are multiple VCOs to supply RF signals for the multiple RF bands.For example, VCO 262 supplies an RF local oscillator signal (for any RFchannel in or the center frequency) for the 2.4 GHz unlicensed band, VCO264 supplies an RF local oscillator signal (for any RF channel in or thecenter frequency) for the low 5 GHz unlicensed band, and VCO 266supplies an RF local oscillator signal (for any RF channel in or thecenter frequency) for the high 5 GHz unlicensed band.

An interface and control block 279 interfaces a clock signal, datasignals and an enable signal to/from an external device, such as abaseband processor and/or a control processor. Transceiver controlsignals sourced from an external device may be coupled to theappropriate transceiver components through the interface control block290 or coupled to pins that are tied to the appropriate components. Thetransceiver control signals include, for example, an RF center frequencycontrol signal, a filter bandwidth control signal, a transmit gainadjustment signal, a receive gain adjustment signal and switch controlsignals. The RF center frequency control signal controls which RF band,and the particular RF channel in that band, for which the RF LOsynthesizer 260 and associated VCOs 262, 264 or 267 outputs a localoscillator signal. An example of a frequency synthesizer suitable foruse with the radio transceivers described herein is disclosed incommonly assigned U.S. Provisional Application No. 60/319,518, filedSep. 4, 2002, and entitled “Frequency Synthesizer for Multi-BandSuper-Heterodyne Transceiver Applications.” The filter bandwidth controlsignal controls the variable bandwidth lowpass filters 150, 158, 180 and188 to operate in either a wideband mode (pass the entire frequency bandor other substantial portion of it) or a narrowband mode (pass aportion, such as a single RF channel). The transmit gain control signalscontrol the gain of the variable amplifiers 216 and 236 on the transmitside and the receive gain control signals control the gain of thevariable amplifiers 146 and 176 on the receive side. The switch controlsignals control the position of the switches 106, 108, 110, 112, 114,116, 200 and 202 according to the operating mode of the radiotransceiver 100 and the frequency band of operation.

The majority of the components of the radio transceiver 100 areimplemented in a semiconductor IC. The large dotted line indicates thosecomponents that may be included in the IC; however, additionalcomponents may be implemented in the IC.

With reference to FIGS. 2 and 5, operation of the transceiver 100 willbe described. For example, RFB1 is the 2.4 GHz unlicensed band and RFB2is one of the 5 GHz unlicensed bands. It should be understood that thesame architecture shown in FIG. 2 can be used for other applications,and that the 2.4/5 GHz dual band application is only an example. Forpurposes of this example, the IF is 902.5 MHz, and the frequency outputby the IF LO synth 250 is 1805 MHz; the RF LO synthesizer outputs an RFlocal oscillator signal that ranges from 3319.5 MHz to 4277.5 MHz. Thevariable lowpass filters 150, 158, 180 and 188 are controllable tofilter a variety of bandwidths in the RF band, for example to facilitateMIMO receive processing of signals detected by the antennas 102 and 104in 20 MHz of bandwidth up to 80 MHz or 100 MHz of bandwidth. Similarly,the variable lowpass filters 276, 278, 286 and 288 are controllable tofilter a variety of bandwidths in the RF band, for example to facilitateMIMO transmit processing of baseband signals to be transmitted in 20 MHzof bandwidth up to 80 MHz or 100 MHz of bandwidth. Alternatively, and asdescribed hereinafter in conjunction with FIGS. 13 and 14, the variablelowpass filters 150, 158, 180 and 188 may be shared for receiveprocessing and transmit processing. Generally, the radio transceiver 100is operated in a half-duplex mode during which it does notsimultaneously transmit and receive in either RFB1 or RFB2.

The radio transceiver 100 may also be operated in a non-MIMOconfiguration. For example, the output of only one receive path may beused with the appropriate variable lowpass filter set to sample anyportion or all of the desired RF band for obtaining data to analyzingsome or all of the spectrum of that RF band.

The T/R switches and band select switches in the RF front-end section105 (FIG. 5) are controlled according to whether the radio transceiveris transmitting or receiving, and in which RF band it is operating.

For example, when the radio transceiver 100 is receiving in RFB1,switches 106 and 108 are moved to their top positions to select thereceive side of the transceiver 100. The RF LO synthesizer 260 iscontrolled to output RF local oscillator signals that will downconvert aparticular (sub-band) from RFB1. Switches 110 and 112 are moved to theirtop positions to select bandpass filters 120 and 124 (associated withRFB1) and corresponding branches of the receiver circuits 140 and 170.Filter 120 bandpass filters the signal detected by antenna 102 andfilter 124 bandpass filters the signal detected by antenna 104. Thelowpass filters 150, 158, 180 and 188 are controlled to operate in thedesired bandwidth. The two signals detected by antennas 102 and 104 maybe spatially diverse signal components of the same transmit signal. Thesignal from antenna 102 is downconverted to IF by mixer 144, filtered bythe IF filter 145, then downconverted to baseband I and Q signals byquad mixers 148 and 156 and filtered by lowpass filters 150 and 158.Each I and Q signal derived from this signal is sample-and-held andalternately selected for output to an ADC by switch 200.

The receiver circuit 170 performs a similar operation for the signaldetected by antenna 104.

The radio transceiver 100 performs MIMO transmit operation in a similarmanner. The LPFs 276, 278, 286 and 288 in the transmitter (or the sharedLPFs of the receiver) are controlled to filter the desired bandwidth. Inaddition, the RF LO synth 260 is controlled to output an RF localoscillator signal according to which frequency band the signals are tobe transmitted. Assuming a signal is to be transmitted on a channel inRFB2, the switches 106 and 108 are moved to their bottom positions,selecting the transmit side of the radio transceiver 100. The switches114 and 116 are moved to their bottom positions, selecting the branch oftransmit circuits 210 and 230 associated with RFB2. The analog basebandsignal to be transmitted consists of first and second signal components,to be transmitted simultaneously by the respective antennas 102 and 104.The appropriate RF local oscillator signal is output to the mixers 218and 238. The I and Q signals of a first transmit signal component areupconverted to IF by quad mixers 212 and 214. The variable amplifier 216adjusts the gain of the resulting IF signal, and the mixer 218upconverts the IF signal to RF. The filter 224 bandpass filters the RFsignal output by the mixer 218 and the power amplifier 228 amplifies theoutput of the bandpass filter 224. Lowpass filter 130 filters theharmonics of the output of the power amplifier 228, and the resultingoutput is coupled to the antenna 102 via switches 114 and 106. A similaroperation occurs for the I and Q signals of the second transmit signalcomponent. The bandpass filter 246 filters the RF signal and the poweramplifier 248 amplifies the filtered signal, which is then coupled tothe lowpass filter 134. The resulting filtered signal is coupled toantenna 104 via switches 116 and 108.

FIG. 3 shows a radio transceiver 100′ that is similar to radiotransceiver 100 except that it employs a variable or walking IFarchitecture, rather than a super-heterodyne architecture. Particularly,in the receiver circuits of the radio transceiver 100′, the received RFsignal is downmixed to an intermediate frequency that depends on the RFlocal oscillator signal, and an IF filter is not needed or is optional.A similar principle applies for the transmit circuits. Therefore, the RFlocal oscillator signal output of the RF LO synthesizer 260 is coupledto a divide-by-four circuit 265 which in turn supplies an IF localoscillator signal to mixers 148 and 156 in receiver circuit 140, mixers178 and 186 in receiver circuit 170, mixers 212 and 214 in the transmitcircuit 210 and mixers 232 and 234 in the transmit circuit 230. Thedivide-by-four circuit 265 generates the IF local oscillator signalbased on the RF local oscillator signal supplied by the RF LOsynthesizer 260. No IF filters are needed and only a single synthesizer(for the RF local oscillator signal) is required. Otherwise, theoperation of the radio transceiver 100′ is similar to that of radiotransceiver 100.

The radio transceivers of FIGS. 2 and 3 have certain advantages thatmake them suitable for highly integrated and low cost implementations.First, the super-heterodyne architecture of FIG. 2 and the walking IFarchitecture of FIG. 3 allow for integrating the power amplifiers in thetransmitter of the radio transceiver IC. This is because the poweramplifier output frequency falls significantly outside the VCO turningrange, thereby avoiding injection locking of the VCO. This is not aseasily possible in other architectures, such as the direct conversionarchitecture shown in FIG. 4. Second, the walking IF transceiver of FIG.3 does not require an IF filter which reduces the bill of materials costof the radio transceiver. Even the super-heterodyne design of FIG. 2 canbe implemented without an IF filter under certain design parameters. Thedesign of FIG. 3 has both the advantage of more easily integrating thepower amplifiers as well as not requiring an IF filter. Therefore, theradio transceiver design of FIG. 3 may be desirable where cost,integration and IC size are important.

Referring now to FIG. 4, a direct-conversion radio transceiverarchitecture 300 is described. Like radio transceiver 100, radiotransceiver 300 has multiple receiver circuits 310 and 340 in thereceiver and multiple transmit circuits 370 and 400 in the transmitter.The receiver circuits are identical and the transmit circuits areidentical. In the receiver circuit 310, there are two amplifiers 312 and314 both coupled to a switch 316. Amplifier 312 receives a bandpassfiltered signal in frequency band RFB1 from a bandpass filter in the RFfront end section 105 (FIG. 2), and similarly amplifier 314 receives abandpass filtered signal in frequency band RFB2. The output of theswitch 316 is coupled to a variable amplifier 318 to adjust the gain ofthe signal supplied to its input. The output of the variable amplifier318 is coupled to mixers 320 and 322 that down-mix the amplified receivesignal by IF local oscillator signals to produce I and Q signals. Theoutput of mixer 320 is coupled to a lowpass filter 324, and the outputof mixer 322 is coupled to a lowpass filter 326. The lowpass filters 324and 326 are, for example, third order lowpass filters that may belocated off-chip from the remainder of the transceiver components forbetter linearity. The outputs of lowpass filters 324 and 326 are coupledto variable lowpass filters 328 and 330, respectively. Variable lowpassfilters 328 and 330 can be controlled to vary their cut-off frequency soas to select either a narrowband (e.g., 10 MHz) or a wideband (e.g., 40MHz). The variable lowpass filters 328 and 330 are coupled tosample-and-hold circuits 332 and 334, respectively. The output of thesample-and-hold circuits 332 and 334 are baseband I and Q signalsrepresenting the signal detected by antenna 102. A switch 336 iscontrolled to alternately select between the baseband I and Q signalsfor coupling to a single ADC, saving the cost of a second ADC.

Receiver circuit 340 has components 342 through 366 which are the sameas the components in receiver circuit 310. Receiver circuits 310 and 340perform a direct-conversion or zero-intermediate frequencydownconversion of the detected RF signals to baseband. To summarize, thefirst receiver circuit 310 has a first downconverter comprising quadmixers 320 and 322 that down-mix a first receive signal detected byantenna 102 directly to baseband I and Q signals. Likewise, the secondreceiver circuit 340 has a second downconverter comprising quad mixers350 and 352 that down-mix a second receive signal detected by antenna104 directly to baseband I and Q signals.

It will be appreciated by those with ordinary skill in the art that inthe receiver circuits 310 and 340, quad mixers 320 and 322, and quadmixers 350 and 352 may be broadband mixers capable of covering both RFB1and RFB2, or alternatively separate quad mixers may be provided for eachRF band.

On the transmit side, transmit circuit 370 comprises first and secondsample-and-hold circuits 372 and 374 that receive I and Q data signalsfor a first transmit signal from switch 371. The outputs of thesample-and-hold circuits 372 and 374 are coupled to the lowpass filters376 and 378. The outputs of the lowpass filters 376 and 378 are coupledto quad mixers 380 and 382, respectively. The quad mixers 380 and 382up-mix the filtered I and Q signals output by the lowpass filters 376and 378 to output RF I and Q signals which are combined and coupled to avariable amplifier 384. The variable amplifier 384 adjusts the gain ofthe first RF signal and supplies this signal to bandpass filters 386 and388, associated with RFB1 and RFB2, respectively. The outputs ofbandpass filters 386 and 388 are coupled to power amplifiers 394 and396. Power amplifiers 390 and 392 amplify the RF signals for frequencybands RFB1 and RFB2 which are coupled to the RF front end 105.

Transmit circuit 400 has components 402 through 422 that are the same asthose in transmit circuit 370. The input to transmit circuit 400consists of I and Q signals for a second transmit signal alternatelysupplied by switch 401. Thus, to summarize, the first transmit circuit370 comprises an upconverter consisting of quad mixers 380 and 382 thatdirectly up-mix baseband I and Q signals to RF I and Q signals that arecombined to form a first RF signal. The second transmit circuit 400comprises an upconverter consisting of quad mixers 410 and 412 thatdirectly up-mix baseband I and Q signals to RF I and Q signals that arecombined to form a second RF signal.

A dual modulus phase-lock loop (PLL) 430, VCOs 432, 434 and 436, asquaring block 438 and a 90° phase shifter 440 may be provided to supplythe appropriate in-phase and quadrature RF local oscillator signals tothe mixers 320 and 322, respectively, in receiver circuit 310; mixers350 and 352 in receiver circuit 370; mixers 380 and 382, respectively,in transmit circuit 370; and mixers 410 and 412, respectively, intransmit circuit 400. The dual modulus PLL 430 is a standard componentfor generating high frequency signals. The squaring block 438 acts as afrequency doubler, reducing pull of the VCO by the power amplifiers. Forexample, in order to provide RF mixing signals for the 2.4 GHzunlicensed band and the high and low 5 GHz unlicensed band, the VCO 432produces an RF signal in the range 1200 through 1240 MHz, VCO 434produces an RF signal in the range 2575 through 2675 MHz, and VCO 436produces an RF signal in the range 2862 through 2912 MHz.

Like radio transceiver 100, there are control signals that are coupledto the appropriate components to control the operation. Radiotransceiver 300 has the same modes of operation as radio transceiver100. There are filter bandwidth control signals to control the variablelowpass filters 328, 330, 358 and 360 depending on the bandwidth ofoperation of the transceiver 300. There are receive gain control signalsto control the variable amplifiers 318 and 348. There are switch controlsignals to control the various switches in the radio transceiver 300 andfront-end section, depending on whether it is in the receive mode ortransmit mode, and depending on which band, RFB1 or RFB2, thetransceiver is operating in. There are RF center frequency controlsignals to control the dual-modulus PLL 410 and VCOs 412-416 dependingon which RF band and RF channel in that band the transceiver isoperating in. There are transmit gain control signals to control thevariable amplifiers 384 and 414 in the transmit circuits.

FIGS. 6-10 illustrate alternative front-end sections. In FIG. 6, thefront-end 500 section comprises many of the same components as front-endsection 105, albeit in a slightly different configuration. The LPFs 128,130, 132 and 134 may be integrated on the radio transceiver IC orincorporated in the radio front-end 500. Instead of switches 106 and108, diplexers 502 and 504 are used for band selection from the antennas102 and 104. As known in the art, a diplexer is a 3-port device that hasone common port and two other ports, one for high frequency signals andone for lower frequency signals. Thus, the diplexers 106 and 108 serveas band select switches. In the example of FIG. 6, the two bands thatare supported are the 2.4 GHz band and the 5.25 GHz band. Switches 110,112, 114 and 116 are transmit/receive switches that select theappropriate signals depending on whether the radio transceiver istransmitting or receiving. For example, when the radio transceiver istransmitting a signal in the 2.4 GHz band through antennas 102 and 104,the diplexer 502 receives the first 2.4 GHz transmit signal from switch110 and couples it to the antenna 102, and the diplexer 504 receives thesecond 2.4 GHz transmit signal from switch 114 and couples it to antenna104. All the other switch positions are essentially irrelevant.Likewise, when receiving a signal in the 5.25 GHz band, diplexer 502couples the first 5.25 GHz receive signal from antenna 102 to switch 112and diplexer 504 couples the second 5.25 GHz receive signal from antenna104 to switch 116. Switch 112 selects the output of the diplexer 502 andswitch 116 selects the output of the diplexer 504.

As is known in the art, the radio transceiver is coupled to a basebandprocessor that may be a separate integrated circuit as shown by thebaseband integrated circuit (BBIC) 510 in FIGS. 6 and 7.

FIG. 7 illustrates a front-end section 500′ that is similar to front-endsection 500 except that the transmit/receive switches are effectivelyintegrated on the radio transceiver IC. Many techniques are known tointegrate switches similar to the transmit/receive switches on the radiotransceiver IC. When the transmit/receive switches are integrated on theradio transceiver IC, for each antenna, a quarter-wave element 515 isprovided in the radio front-end 500′ at each band branch off of thediplexer for each antenna. FIG. 8 shows this configuration for oneantenna 102 only as an example, but it is repeated for each antenna.When a signal is being transmitted, the transmit/receive switch isswitched to the terminal that is connected to ground so that the signaloutput by the corresponding power amplifier (PA) of the transmitter isselected and coupled to the diplexer, and when a signal is received, itis switched to the other terminal so that the receive signal passesthrough the quarter-wave element 525, the transmit/receive switch andpasses to the LNA in the receiver. The quarter-wave element 515 may beany quarter-wave transmission line. One example of an implementation ofthe quarter-wave element 515 is a microstrip structure disposed on aprinted circuit board. The quarter-wavelength characteristic of thequarter-wave element 515 creates a phase shift that acts as an impedancetransformer, either shorting the connection between the bandpass filterand ground, or creating an open circuit, depending on the position ofthe switch.

The radio transceiver IC and front-end configurations shown in FIGS. 6and 7 are useful for network interface cards (NICs) to serve as an802.11× WLAN station.

FIG. 9 illustrates a front-end section 600 that interfaces with tworadio transceiver ICs to provide a 4 path MIMO radio transceiver device.One example of a use for this type of configuration is in an accesspoint (AP) for a WLAN. Whereas the radio transceiver configurationsdescribed up to this point were for 2-path MIMO operation, 4-path MIMOoperation provides even greater link margin with other devices when usedin connection with the maximal ratio combining schemes referred toabove.

The front-end section 600 interfaces two radio transceiver ICs to eightantennas 602 through 616. A BBIC 660 is coupled to the two radiotransceiver ICs that operate in tandem to transmit 4 weighted componentsof a single signal or to receive 4 components of a single receivedsignal. Antennas 602, 606, 610 and 614 are dedicated to one frequencyband, such as the 2.4 GHz band and antennas 604, 608, 612 and 616 arededicated to another frequency band, such as a 5 GHz band. In thefront-end section 600, there are transmit/receive switches eight 620through 634 each associated with one of the antennas 602 through 616respectively. There are also eight bandpass filters 640 through 654coupled to respective ones of the transmit/receive switches 620 through634. The transmit/receive switches 620 through 634 could be integratedon the respective radio transceiver ICs instead of being part of thefront-end section 600. Though not specifically shown, the LPFs are alsointegrated on the radio transceiver ICs. Operation of the front-endsection 600 is similar to what has been described above. Thetransmit/receive switches 620 through 634 are controlled to select theappropriate signals depending on whether the radio transceiver ICs areoperating in a transmit mode or a receive mode.

FIG. 10 illustrates a front-end section 600′ that is similar tofront-end section 600 but excludes the transmit/receive switches.Moreover, the radio transceiver 670 is a single IC that integrates4-paths (what is otherwise included on two radio transceiver ICs asshown in FIG. 9). The transmit/receive switches are integrated on theradio transceiver IC 670. The operation of the front-end section 600′ issimilar to that of front-end section 600. FIG. 10 illustrate the abilityto scale the number of MIMO paths to 3, 4 or more separate paths.

FIGS. 9 and 10 also illustrate the radio transceivers 100, 100′ and 300deployed in multiple instances to support multiple channel capability ina communication device, such as an AP. For example, as shown in FIG. 9,one radio transceiver, such as an access point, could perform 2-pathMIMO communication with devices on a channel while the other radiotransceiver would perform 2-path MIMO communication with devices onanother channel. Instead of interfacing to one baseband IC, each wouldinterface to a separate baseband IC or a single baseband IC capable ofdual channel simultaneous operation.

FIGS. 11 and 12 show a configuration whereby the number of DACs and ADCsthat are coupled to the radio transceiver can be reduced. Normally, aseparate DAC or ADC would be required for every signal that requiresprocessing. However, in a half-duplex radio transceiver, since transmitand receive operations are not concurrent, there is opportunity forsharing DACs and ADCs. For example, FIG. 11 shows a configurationcomprising two ADCs 710 and 720 and three DACs 730, 740 and 750. ADC 720and DAC 730 are shared. Switch 760 selects input to the ADC 720 andswitch 770 selects the output of the DAC 730. A digital multiplexer(MUX) 780 is coupled to the ADC 720 to route the output therefrom, andto the DAC 730 to coordinate input thereto. The ADCs, DACs and digitalMUX 780 may reside on a separate integrated circuit from the radiotransceiver integrated circuit. For example, these components may resideon the baseband integrated circuit where a baseband demodulator 790 anda baseband modulator 795 reside.

The number of ADCs is reduced by using a single ADC 720 to digitize boththe received Q signal and the transmit power level signal. Similarly,the number of DACs is reduced by sharing a single DAC 730 to convertboth the transmit I signal and the receiver gain control signal. Thedigital MUX 780 selects the signal (either the transmit I signal or thereceiver gain control signal) that is supplied as input to the sharedDAC 730. Similarly, the signal that is output by the shared ADC 720(digital received Q signal or the digital transmit power level signal)is routed to the appropriate destination by the digital MUX 780.

As described above, one way to facilitate sharing of the ADC and the DACis to provide switches 760 and 770. These switches may reside on theradio transceiver IC. An output terminal of switch 760 is coupled to theshared ADC 720, one input terminal is coupled to the LPF at the outputof the local oscillator that generates the received Q signal and theother input terminal is coupled to the output of the power detector thatgenerates the transmit power level signal. Switch 760 is controlled toselect one of two positions, depending on whether the ADC is to be usedfor the received Q signal or the transmit power level signal. Likewise,an input terminal of switch 770 is coupled to the shared DAC 730, oneoutput terminal is coupled to the variable power amplifier in thereceiver and the other output terminal is coupled to the LPF thatsupplies a transmit I signal to the in-phase local mixer in thetransmitter. Switch 770 is controlled to select one of two positions,depending on whether the shared DAC is to be used for the receiver gaincontrol signal or the transmit I signal. The configuration shown in FIG.11 can be repeated for each receive path/transmit path pair in thetransceiver.

It should be understood that the switches 760 and 770 are optional. Asshown in FIG. 12, they may be replaced with common signal paths if theradio transceiver IC is a half-duplex transceiver, meaning that thereceiver and transmitter are not operational at the same time.Therefore, the shared DAC 730, for example, will convert whicheverdigital signal is supplied to it (the transmit I signal or the receivergain control signal, depending on whether the transceiver is in receivemode or transmit mode), and the DAC 730 will output the analog versionof that signal on both paths. If the transmit I signal is selected forprocessing by the shared DAC 730, the receiver will be off, so couplinga analog version of the transmit I signal to the variable poweramplifier in the receive channel will have no effect, but it also willbe coupled to the in-phase local oscillator in the transmitter, which isdesired. A similar situation holds true if the switch for the shared ADC720 is replaced with a common signal path configuration.

A single ADC and a single DAC can be shared among signals from thetransmitter and receiver (since in a half-duplex transceiver, thetransmitter and receiver are generally not operational at the sametime). The signals that are identified above are only examples of thetransmitter and receiver signals that may be multiplexed to a single ADCor single DAC.

FIGS. 13 and 14 illustrate configurations that allow for sharing of theLPFs used to filter the baseband receive signals and baseband transmitsignals in the radio transceivers of FIGS. 2-4. As an example, a singleantenna path of the direct conversion radio transceiver 300 is selectedto illustrate the filter sharing technique. Some intermediatecomponents, such as variable amplifiers and sample-and-hold circuits,are not shown for simplicity. LPFs 328 and 330 are shared to both filterthe received I and Q signals (RX I and RX Q) associated with an antenna,such as antenna 102, and filter the baseband transmit I and Q signals(TX I and TX Q) to be transmitted. The switches 710 and 720 each havetwo input terminals and an output terminal coupled to the input of theLPFs 328 and 330, respectively. Coupled to the input terminals of theswitch 710 are the receive I signal output by the quad mixer 320 and thebaseband transmit I signal. Similarly, coupled to the input terminals ofthe switch 720 are the receive Q signal output by the quad mixer 322 andthe baseband transmit Q signal. A transmit/receive control signal iscoupled to the switches 710 and 720 to cause the switches to selecteither their terminals to which the receive I and Q signals areconnected or the terminals to which the transmit I and Q signals areconnected. In FIG. 13, it is assumed that the output impedance at eachfilter is low and each load impedance is high (typical in most analogICs) so that the output of each filter can be summed. Therefore, only asingle multiplexer is needed at the input to the filters. Theconfiguration of FIG. 14 is similar to FIG. 15, except that additionalswitches 730 and 740 are provided in case the impedances are not asdescribed above.

In sum, a multiple-input multiple-output (MIMO) radio transceiver isprovided comprising a receiver and a transmitter. The receiver comprisesat least first and second receiver circuits each to process a signalfrom a corresponding one of first and second antennas. The firstreceiver circuit comprises a first downconverter coupled to the firstantenna to downconvert a first receive signal detected by the firstantenna to produce a first baseband signal; and a first lowpass filtercoupled to the first downconverter that lowpass filters the firstbaseband signal. The second receiver circuit comprises a seconddownconverter coupled to the second antenna to downconvert a secondreceive signal detected by the second antenna to produce a secondbaseband signal; and a second lowpass filter coupled to the seconddownconverter that lowpass filters the second baseband signal. Thetransmitter comprises at least first and second transmitter circuitseach of which processes a signal to be transmitted by a correspondingone of the first and second antennas. The first transmitter circuitcomprising a first upconverter that upconverts a first baseband analogsignal to generate a first RF frequency signal; a first bandpass filtercoupled to the output of the first upconverter that filters the first RFfrequency signal; and a first power amplifier coupled to the output ofthe bandpass filter that amplifies the filtered RF frequency signal toproduce a first amplified signal that is coupled to the first antennafor transmission. Similarly, the second transmitter circuit comprises asecond upconverter that upconverts a second baseband analog signal togenerate a second RF frequency signal; a second bandpass filter coupledto the output of the second upconverter that filters the second RFfrequency signal; and a second power amplifier coupled to the output ofthe second bandpass filter that amplifies the second filtered RFfrequency signal to produce a second amplified signal that is coupled tothe second antenna for transmission.

Similarly, a multiple-input multiple-output (MIMO) radio transceiver isprovided comprising a receiver comprising at least first and secondreceiver circuits each to process a signal from a corresponding one offirst and second antennas, and a transmitter. The first receiver circuitcomprises a first downconverter coupled to the first antenna todownconvert a first receive signal detected by the first antenna toproduce a first in-phase baseband signal and a first quadrature-phasebaseband signal; and first and second lowpass filters coupled to thefirst downconverter that lowpass filter the first in-phase basebandsignal and the first quadrature phase baseband signal, respectively. Thesecond receiver circuit comprises a second downconverter coupled to thesecond antenna to downconvert a second receive signal detected by thesecond antenna to produce a second in-phase baseband signal and a secondquadrature-phase baseband signal; and third and fourth lowpass filterscoupled to the second downconverter that lowpass filter the secondin-phase baseband signal and the second quadrature-phase basebandsignal. The transmitter comprises at least first and second transmittercircuits each of which processes a signal to be transmitted by acorresponding one of the first and second antennas. The firsttransmitter circuit comprises a first upconverter that upconverts afirst in-phase baseband analog signal and a first quadrature-phasebaseband analog signal to generate a first RF frequency signal; a firstbandpass filter coupled to the output of the first upconverter thatfilters the first RF frequency signal; and a first power amplifiercoupled to the output of the first bandpass filter that amplifies thefirst filtered RF frequency signal to produce a first amplified signalthat is coupled to the first antenna for transmission. The secondtransmitter circuit comprises a second upconverter that upconverts asecond in-phase baseband analog signal and a second quadrature-phasebaseband analog signal to generate a second RF frequency signal; asecond bandpass filter coupled to the output of the second upconverterthat filters the second RF frequency signal; and a second poweramplifier coupled to the output of the second bandpass filter thatamplifies the second filtered RF frequency signal to produce a secondamplified signal that is coupled to the second antenna for transmission.

While the foregoing description has referred to a MIMO radio transceiverwith two antennas, and thus two receiver circuits and two transmittercircuits, it should be understood that the same concepts describedherein may be extended in general to a radio transceiver with Ntransmitter circuits and N transmitter circuits for operation with Nantennas.

The above description is intended by way of example only.

1. A radio transceiver comprising: a single semiconductor integratedcircuit including: a first receiver circuit configured to receive asignal having a first center frequency from a first antenna, and todownconvert the signal from the first antenna to produce a first receivebaseband signal; a second receiver circuit configured to receive asignal having the first center frequency from a second antenna, thesecond antenna spatially separate from the first antenna, the secondreceiver circuit configured to downconvert the signal from the secondantenna to produce a second receive baseband signal substantiallysimultaneously as the first receiver circuit downconverts the signalfrom the first antenna; a first transmitter circuit configured toreceive a first transmit baseband signal and to upconvert the firsttransmit baseband signal to produce a first radio frequency signal witha second center frequency for transmission over the first antenna; and asecond transmitter circuit configured to receive a second transmitbaseband signal, the and to upconvert the second transmit basebandsignal to produce a second radio frequency signal with the second centerfrequency for transmission over the second antenna substantiallysimultaneously as the transmission of the first radio frequency signalover the first antenna.
 2. The radio transceiver of claim 1 wherein thefirst receive baseband signal and the second receive baseband signal areweighted and combined.
 3. The radio transceiver of claim 1 wherein thefirst receive baseband signal and the second receive baseband signal areweighted and combined by maximal ratio combining.
 4. The radiotransceiver of claim 1 wherein the first transmit baseband signal andthe second transmit baseband signal are weighted components of a singletransmit signal.
 5. The radio transceiver of claim 1 wherein a bandwidthof the received signals from the first and second antenna varies and abandwidth of the first and second radio frequency signal varies.
 6. Theradio transceiver of claim 5 wherein the bandwidth range is from 20 MHzto 100 MHz.
 7. The radio transceiver of claim 1 wherein the receivedsignals of the first antenna are of a first bandwidth, the receivedsignals of the second antenna are of a second bandwidth, the firstbandwidth different than the second bandwidth.
 8. The radio transceiverof claim 7 wherein the first bandwidth is 20 MHZ and the secondbandwidth is 80 MHz.
 9. The radio transceiver of claim 1 wherein thefirst and second transmitter circuits have transmit processing pathsthat are amplitude matched and the first and second receiver circuitshave receive processing paths that are amplitude matched.
 10. The radiotransceiver of claim 1 wherein semiconductor integration of the singlesemiconductor integrated circuit is performed such that transmitprocessing paths of the first and second transmitter circuits areamplitude and phase response matched and the receive processing paths ofthe first and second receiver circuits are amplitude and phase responsematched.
 11. The radio transceiver of claim 1 wherein changes intemperature are amplitude response are tracked between receive tracks ofthe first and second receiver circuit and between transmit paths of thefirst and second transmitter circuit.
 12. The radio transceiver of claim1 wherein each of the first and second receiver circuits has a separatein-phase receiver path and a separate quadrature receiver path.
 13. Theradio transceiver of claim 1 wherein each of the first and secondtransmitter circuits has a separate in-phase transmitter path and aseparate quadrature phase transmitter path.
 14. The radio transceiver ofclaim 1 wherein the second receiver and second transmitter circuit arenot used when multiple input multiple output processing is not required.15. The radio transceiver of claim 1 wherein the single semiconductorintegrated circuit comprises a voltage controlled oscillator thatproduces a radio frequency local oscillator signal for use by mixers fordownconverting the first antenna and the second antenna received signalhaving the first center frequency.
 16. The radio transceiver of claim 1wherein the single semiconductor integrated circuit comprises a voltagecontrolled oscillator that produces a radio frequency local oscillatorsignal for use by mixers for upconverting the first and second transmitbaseband signal to the second center frequency.
 17. The radiotransceiver of claim 1 wherein the single semiconductor integratedcircuit comprises an intermediate frequency synthesizer, theintermediate frequency synthesizer produces an intermediate frequencyoscillator for use by mixers for downconverting the first antenna andthe second antenna received signal.
 18. The radio transceiver of claim 1wherein the single semiconductor integrated circuit comprises anintermediate frequency synthesizer, the intermediate frequencysynthesizer produces an intermediate frequency oscillator for use bymixers for upconverting the first and second transmit baseband signal.19. The radio transceiver of claim 1 wherein the single semiconductorintegrated circuit comprises an intermediate frequency synthesizer, theintermediate frequency synthesizer produces an intermediate frequencyoscillator for use by mixers for downconverting the first antenna andthe second antenna received signal and for use by mixers forupconverting the first and second transmit baseband signal.
 20. Theradio transceiver of claim 1 further comprising a baseband integratedcircuit for baseband processing the first and second receive basebandsignals and for producing the first and second transmit basebandsignals.
 21. The radio transceiver of claim 1 further comprising asecond single semiconductor integrated circuit of substantiallyidentical configuration as the single semiconductor integrated circuitand processing for a third and fourth antennas spatially separate fromthe first and second antennas.
 22. The radio transceiver of claim 23wherein a single baseband integrated circuit for baseband processing thefirst and second receive baseband signals and third and fourth receivebaseband signals produced by the second single semiconductor integratedcircuit and the single baseband integrated circuit for producing thefirst and second transmit baseband signals and third and fourth basebandsignals for use by the second single semiconductor integrated circuit.23. The radio transceiver of claim 1 wherein each of the first andsecond receiver circuits comprises a downconverter for downconvertingthe signal from a corresponding one of the first and second antennas anda filter for filtering the downconverted signal.
 24. The radiotransceiver of claim 23 wherein the filter is a lowpass filter.
 25. Theradio transceiver of claim 23 wherein the signal from the correspondingone of the first and second antennas is filtered by a bandpass filterprior to processing by the down converter.
 26. The radio transceiver ofclaim 23 wherein the downconverter comprises a radio frequency mixerwhich mixes the signal of the corresponding one of the first and secondantennas with a radio frequency local oscillator to produce a basebandsignal.
 27. The radio transceiver of claim 23 wherein the downconvertercomprises a radio frequency mixer which mixes the signal of thecorresponding one of the first and second antennas with a radiofrequency local oscillator to produce an intermediate frequency signaland an intermediate frequency mixer which mixes the intermediatefrequency signal with an intermediate frequency local oscillator toproduce a baseband signal.
 28. The radio transceiver of claim 1 whereineach of the first and second transmitter circuits comprises anupconverter which upconverts a corresponding one of the first and secondtransmit baseband signals.
 29. The radio transceiver of claim 28 whereineach of the first and second transmitter circuits comprises a filterthat filters the corresponding one of the first and second transmitbaseband signal.
 30. The radio transceiver of claim 29 wherein thefilter is a lowpass filter.
 31. The radio transceiver of claim 28wherein each of the first and second transmitter circuits comprises afilter coupled to a power amplifier which process a corresponding one ofthe first and second radio frequency signals.
 32. The radio transceiverof claim 31 wherein the filter is a bandpass filter.
 33. The radiotransceiver of claim 32 wherein the bandpass filter is operativelycoupled to the upconverter and the power amplifier is coupled to anoutput of the bandpass filter.
 34. The radio transceiver of claim 28wherein the upconverter comprises a radio frequency mixer which mixesthe corresponding one of the first and second transmit baseband signalswith a radio frequency local oscillator.
 35. The radio transceiver ofclaim 28 wherein the upconverter comprises an intermediate frequencymixer which mixes the corresponding one of the first and second transmitbaseband signals with an intermediate frequency local oscillator and aradio frequency mixer which mixes the corresponding one of the first andsecond transmit baseband signals with a radio frequency localoscillator.
 36. A multiple-input multiple-output transceiver comprising:a single integrated circuit comprising: a first receiver circuitconfigured to receive a first received signal from a first antenna, thefirst receiver circuit configured to downconvert the first receivedsignal to produce a first receive baseband signal; a second receivercircuit configured to receive a second received signal from a secondantenna, the first and second received signals being spatially diverseversions of a transmitted signal, the second receiver circuit configuredto downconvert the second received signal to produce a second receivebaseband signal; a first transmitter circuit configured to receive afirst transmit baseband signal, the first transmitter circuit configuredto upconvert the first transmit baseband signal to produce a first radiofrequency signal, the first radio frequency signal for transmission overthe first antenna; and a second transmitter circuit configured toreceive a second transmit baseband signal, the second transmittercircuit configured to upconvert the second transmit baseband signal toproduce a second radio frequency signal, the second radio frequencysignal for transmission over the second antenna, the first and secondradio frequency signal for transmission as a multiple-inputmultiple-output waveform over the first and second antennas.
 37. Asingle integrated circuit comprising: a first downconverter configuredto receive a first received signal from a first antenna and configuredto downconvert the first received signal to produce a first receivebaseband signal; a second downconverter configured to receive a secondreceived signal from a second antenna, the first and second receivedsignals being spatially diverse versions of a transmitted signal, thesecond downconverter configured to downconvert the second receivedsignal to produce a second receive baseband signal; a first upconverterconfigured to upconvert a first transmit baseband signal to produce afirst radio frequency signal, the first radio frequency signal fortransmission over the first antenna; and a second upconverter configuredto upconvert a second transmit baseband signal to produce a second radiofrequency signal, the second radio frequency signal for transmissionover the second antenna, the first and second radio frequency signalsfor transmission as a multiple-input multiple-output waveform over thefirst and second antennas.
 38. A multiple-input multiple-outputcommunication device comprising: at least a first and second antenna; aradio front end configured to receive a first received signal from thefirst antenna and a second received signal from the second antenna andconfigured to provide the first and second received signal to a singleintegrated circuit, the first and second received signals beingspatially diverse versions of a transmitted signal, the radio front endconfigured to receive a first radio frequency signal and a second radiofrequency signal and the radio front end configured to provide the firstradio frequency signal for transmission over the first antenna andconfigured to provide the second radio frequency signal for transmissionover the second antenna, the first and second radio frequency signalsfor transmission as a multiple-input multiple-output waveform over thefirst and second antennas; the single integrated circuit comprising: afirst receiver circuit configured to receive the first received signal,the first receiver circuit configured to downconvert the first receivedsignal to produce a first receive baseband signal; a second receivercircuit configured to receive the second received signal, the secondreceiver circuit configured to downconvert the second received signal toproduce a second receive baseband signal; a first transmitter circuitconfigured to receive a first transmit baseband signal, the firsttransmitter circuit configured to upconvert the first transmit basebandsignal to produce the first radio frequency signal; and a secondtransmitter circuit configured to receive a second transmit basebandsignal, the second transmitter circuit configured to upconvert thesecond transmit baseband signal to produce the second radio frequencysignal.
 39. The multiple-input multiple-output communication device ofclaim 38 further comprising a baseband processor configured to perform aweighted combining of the first and second receive baseband signals andconfigured to provide the first and second transmit baseband signals.40. The multiple-input multiple-output communication device of claim 39further comprising a third and fourth antennas, a second singleintegrated circuit for processing signals of the third and fourthantennas and the baseband processor configured to baseband processbaseband signals associated with the third and fourth antennas.
 41. Theradio transceiver of claim 1 further comprising: a first switch withinputs coupled to the first and second receiver circuits and a commonoutput configured to output either the first baseband signal or thesecond baseband signal; and a second switch with outputs coupled to thefirst and second transmitter circuits and a common input configured toinput a baseband analog signal to either the first transmitter circuitor the second transmitter circuit.
 42. The radio transceiver of claim 1,and further comprising a first power amplifier in the first transmittercircuit coupled to the output of the first upconverter that amplifiesthe first RF signal and a second power amplifier in the secondtransmitter circuit coupled to the output of the second upconverter thatamplifies the second RF signal.
 43. The radio transceiver of claim 1,and further comprising a first bandpass filter coupled between theoutput of the first upconverter and an input to the first poweramplifier that filters the first RF signal, and a second bandpass filtercoupled between the output of the second upconverter and an input to thesecond power amplifier that filters the second RF signal.
 44. The radiotransceiver of claim 1, wherein the first and second downconvertersdownconvert the first and second receive signals directly to baseband.45. The radio transceiver of claim 1, wherein each of the first andsecond downconverters comprises an RF mixer that down-mixes the firstand second receive signals, respectively, to an intermediate frequencysignal, and a pair of quad mixers that down-mix the intermediatefrequency signal to in-phase and quadrature baseband signals.
 46. Theradio transceiver of claim 1, wherein each of the first and secondreceiver circuits further comprises a lowpass filter coupled to theoutput of the first and second downconverters, respectively, whereineach lowpass filter is a variable lowpass filter that is responsive to abandwidth control signal so as to pass a portion of a radio frequencyband or substantially the entire radio frequency band.
 47. The radiotransceiver of claim 1, and further comprising first and second lowpassfilters, the first lowpass filter having inputs and an output and beingshared by the first transmitter circuit and first receiver circuit, tofilter either the first baseband analog signal that is output to thefirst transmitter circuit or to filter the first baseband signalproduced by the first receiver circuit, and the second lowpass filterhaving inputs and an output and being shared by the second transmittercircuit and second receiver circuit to filter either the second basebandanalog signal that is output to the second transmitter circuit or tofilter the second baseband signal produced by the second receivercircuit, and further comprising a first switch having an output coupledto an input of the first lowpass filter and that couples to the input ofthe first lowpass filter either the first baseband analog signal or thefirst baseband signal, and a second switch having an output coupled toan input of the second lowpass filter and that couples to the input ofthe second lowpass filter either the second baseband analog signal orthe second baseband signal.
 48. The radio transceiver of claim 1 furthercomprising a plurality of switches, each switch coupled to one of theplurality of antennas and coupled to one transmitter circuit and onereceiver circuit associated with the one antenna.
 49. The radiotransceiver of claim 1, further comprising: an interface and controlcircuit configured to couple a baseband control with the radiotransceiver.
 50. The radio transceiver of claim 49, wherein theinterface and control circuit is configured to receive at least one of afilter bandwidth control signal, a center frequency control signal, anda switch control signal.
 51. The radio transceiver of claim 1, whereineach receiver circuit is configured to receive a signal of only one ofthe first or second frequency at a time.
 52. The radio transceiver ofclaim 51, wherein the first frequency is 2.4 GHz and the secondfrequency is 5.0 GHz.